| The study is direct by continental dynamics, combined with structural geology, tectonic chronology, chronology reservoir, geophysics and petroleum geology, and use the methods of seismic interpretation, balanced section and reservoir studies analysis, and unites the results of field geological studies, and has the comprehensive, reliable geological, geophysical and geochemical data as the basis. The object of study is a unique tectonic units of the northern margin of Xuefeng Uplifte. The breakthrough points are the giant hydrocarbon accumulation in northern margin of Xuefeng uplift. Analyze the structural characteristics. Clarify the giant hydrocarbon accumulation state and Scale of marine strata. Aeveal the main factors in the massive oil and gas enrichment. Starting from a global perspective, the study reveals a new intracontinental oil and gas enrichment unit, and explore the unique continental dynamics connotation of Chinese-style and the reservoir response.The study describe the regional geophysical characteristics, tectonic evolution, stratigraphic profiles, and basic marine strata conditions for hydrocarbon accumulation firstly, determining the overall framework of the regional geological background.Paleo-reservoirs and hydrocarbon shows along the northern margin of Xuefeng uplift in the marine strata mainly develop in ancient anticline and fault zones, and are controlled by paleo-uplift and tectonization in plane. Be closer to the margin of the uplift, the paleo-reservoirs and hydrocarbon shows are more. The distribution regularities of hydrocarbon shows are closely related to the development of source rocks and hydrocarbon thermal evolution obviously on the vertical strata. The paleo-reservoirs and bituminous shows are mainly seen in Sinian and the lower Paleozoic. Oil and gas shows are mainly in the upper Paleozoic and Mesozoic, especially Permian and Triassic. The occurrences of paleo-reservoirs and hydrocarbon shows and are obviously united controlled by the output state and late transformation-destruction of original reservoirs, and abundant including fracture, pore, geode, dissolution pore and cave, especially fracture (crack) dominated. The occurrences of bituminous and gas shows are mostly fracture, and the occurrences of oil shows are mainly fracture, but geode is also more common. Using the reservoir scale sequential method, the study gets that the total original marine hydrocarbon reservoirs of the northern margin of Xuefeng uplift are 90.5×108 tons. The study suggests two main controlling factors for the massive accumulation. One is two sets of high-quality hydrocarbon source rocks of the Lower Cambrian and the Upper Ordovician-Lower Silurian. The other is two stages of favorable space-time matching relationships for accumulation in the Caledonian cycle and the early of late Indosinian-early Yanshannian cyle.The tectonic layer of Xuefeng uplift and its northern margin can be divided into the basement layer and the cover layers which include several sets of slip layers. Faults and folds systems analysis showe strong differences of its structural system. NE trending fault system is extremely development, which has mainly overthrust nature in Xuefeng segment, and develop overthrust faults and sinistral slip in Miaoling segment. NW trending fault system with left-slip properties develops in the northern margin of Miaoling uplift. Nearly NS-trending fault system only develops in the western margin of Miaoling uplift segment. Xuefeng uplift segment and its northern margin develop trough-like folds and comb-like folds. The folds in Miaoning uplift and its northern margin mainly develop joint construction, and is controlled by boundary faults, and are superimposed by the early folds.Xuefeng uplift and its circumferentia have the structural features of "bulge main thing segmentation in the uplift body and zoning in the north-south. The body of Xuefeng uplift is divided into Xuefeng segment and Miaoling segment. According to tectonic deformation differences, the north and south magrins of the different segments can be divided into different tectonic deformation zone, showing uplifting nuclear portion of the substrate, and standing body or quasi-standing body detach extended to both sides of the pushover, and the base involved in changing the law to cap slippage. Xuefeng uplift presents the overall structure asymmetrical fan. Miaoling uplift and its periphery shows a symmetrical structure, respectively W, E thrusting.The Study then determine and characterize the structural characteristics and evolution of the key construction period of the northern margin of the uplift.Xuefeng uplift and its northern margin has been the intracontinental environment since the Caledonian, and experienced two major tectonic-sedimentary facies and palaeogeography change in Caledonian. The unconformity are bounded by Anhua-Xupu-Jingzhou fracture and the line of Cili-Baojing-Tongren-Guiyang-Zhenyuan in Caledonian. Its subject is weak deformation zone, and its southeast are intense folding deformation zone, and the northwest have the main vertical lifting motion and no significant movement folds, forming a tectonic framework of big depression and big uplift.According to the tectonic sedimentary facies and palaeogeography in the Late Indochina-Early Yanshanian, its show the marine sediments ended. The unconformity in Indosinian are bounded by Cili-Baojing-Tongren-Caili line and Longsan-Hefeng-Caili line, from south east to north west its can be divided into the high angular, slightly angular, and parallel unconformity area. Indochina movement impact westward to Hefeng-Longsan line. East of the line occurr orogenic movement. West of the line mainly occurr vertical movement. Yanshanian movement are bounded by Anhua-Xupu fault and Qiyueshan-Xishui fault breaking. From southeast to northwest, tectonic gradually become the new starting time, and the role of episodic structure gradually become less with progressive deformation characteristics. At the Later Indochina, the tectonic framework are fault-fold structure at the east, and depression-uplift at the west by the line of the northern margin fault-Guiyang line. At the Early Yanshanian, the deformation spreaded to the Qiyueshan fault, and showed strong squeezing action and intracontinental orogeny, and extensively developed folds and thrust faults with thick-skinned structure.Samples apatite fission track thermal geochronology show that the uplift and its northern margin experienced at least three tectonic movements since the Late Jurassic. The first and second parts of tectonic movement occurred at 165-140Ma and 125-72Ma, representing early and late Yanshan Yanshan tectonic movement, and related to the subduction of the ancient Pacific plate to the Eurasian plate and the expansion to the west of the uplift, which led to the uplift and the thrust-fold structure at the northern margin. The third phase of tectonic movement occurred in 45-25Ma, and represent Himalayan movement, related to the collision of the Indian plate and Eurasian plate, and the oblique collision of the Pacific Plate and the Philippine Plate.According to the balanced section kinematic analysis, stratigraphic record, and chronological evidence, the deformation modes of Xuefeng uplift and its northern margin is "three steps" progressive deformation in Mesozoic and Cenozoic. The first step is Xuefeng uplift. The second step is West Hunan-Guizhou northeast fault-fold belt. The third step is East Sichuan tectonic belt. With the progressive deformation from the first step to the third step, the base involved and the degree of uplift gradually weakened and shallow, and the thick-skinned strcture transform to thin-skinned tectonic structure. Miaoling uplift and its northern margin undergoed the uplift at Caledonian uplift. Its kinematic mode can be summarized as two uplifts and two depressions at Paleozoic, and progressive deformation in Mesozoic and Cenozoic. Due to the early involvement of uplift, the transformation of thick-skinned structure to thin-skinned structure is not obvious at the late progressive tectonic deformation process. The shortening deformation and rate in the progressive expansion are differents at Xuefeng uplift and Miaoling uplift respectively, leading to the different of the degree and the way of involvement. At the same extend direction, with the different expend growth rate at different structures and coupled with the difference of the structural system and the base structure at the northern margin, leading to the differences of kinematics in Xuefeng segment and Miaoling segment.The Lower Cambrian and the Upper Ordovician-Lower Silurian source rocks are fine characterization of regional development and key distribution blocks, and evaluated. The ancient tectonic background are rebuild of the hydrocarbon source rocks. The Lower Cambrian developped in intracontinental depression slopes background, and has the development pattern of High productivity Kerogen-Quick transgression-Hydrothermal activity-Ocean currents rise-Anoxic events-Intracontinental depression slopes. The intracontinental tectonic-environment model of the Upper Ordovician-Lower Silurian is highly productive organic matter-Intracontinental depression-Local hypoxia. High productivity organic means productivity conditions. Intracontinental depression are the continental tectonic setting of source rocks. Local hypoxi refers to the preservation of anoxic conditions and regional rather than global.According to the matching relationship of intracontinental tectonics and accumulation, Caledonian is the key construction period of material basis of accumulation and paleo-reservoir, and the Late Indochina-Early Yanshanian period is the key construction and transformation period of accumulation, and the intracontinental tectonics control the difference accumulation. The Lower Cambrian and Upper Ordovician-Lower Silurian were developed in the Caledonian. The former has a intracontinental depression slope tectonic setting. The latter developed in the slop of the northern margin of Xuefeng palaeo-uplift. The unique tectonics setting of the Caledonian controlled the formation and spread of the two sets of source rocks, which determines the ancient reservoirs spatial distribution. The history of the Lower Cambrian hydrocarbon generation and expulsion, the evolution of reservoirs and the history of tectonic development had a good matching relationship at space-time at Caledonian in the northern margin of Xuefeng uplift, which was conducive to the formation of giant hydrocarbon accumulation zone at the northern margin. Under this good relationship of the space-time, hydrocarbon migrated to the favorable area of Majiang and Nanshanping, and accumulated to reservoir, forming the accumulation mode of early accumulation and uplift control. The construction in the Late Indochina-Early Yanshanian include the primary and secondary reservoir. There are two ways of transformation and destruction. First, the settlement and deep burried make the oil phase transform to gas phase. Second, the uplift-denudation at the late of the early Yanshanian caused the transformation and destruction of the most reservoirs. Caledonian and Indochina-early Yanshanian intracontinental tectonic movement show some differences in different regions, resulting in a deposition and fault activity and the difference of thermal evolution of the Lower Cambrian and the accumution period in Majiang and Kaili area. The Lower Cambrian source rocks accumulated in Caledonian and transformed to the high evolution bitumen later in Majiang area. The Lower Cambrian source rocks accumulated in Indosinian and transformed to the low evolution bitumen and residue reservoir later in Kaili area.The regions (zone) of huge amount of hydrocarbon mainly development in the passive continental margin, the active continental margin and the continental rifts in the global, while the northern margin of Xuefeng uplift has the different tectonic setting. Our researches suggest that the superimposed slope about the slop of intra continental depression and the slop of the margin of paleo-uplift at the northern margin of Xuefeng uplift is a new massive enrichment unit of hydrocarbon in the blocks. The superimposed slope with space-time matching is a favorable accumulation area, but also an active transformation area for hydrocarbon. The study suggests that the further understanding of the response relationship between the intra continental evolution and the accumulation and destruction of marine hydrocarbon in South China has an obviously effect to promote the evaluation and exploration of marine hydrocarbon about the northern margin of Xuefeng uplift or the similar continental tectonic belt. |
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